1. Field of the Invention
The present invention relates to an image processor provided with a function for recognizing a specific image, an image processing method and a storage medium storing a program for implementing such a function.
2. Description of the Related Art
Recently, the quality of an image of a color copying machine and a color printer, a function of a personal computer, the quality of an image of a scanner and others have been enhanced and a print of high quality has become relatively easy to prepare. Hereby, a problem is caused that securities such as a bank note and a ticket of which the copying is prohibited can be illegally copied by using these machines.
To mainly prohibit such illegal copying, various methods of recognizing an image of which the printing is prohibited by digital image processing technology are proposed in documents such as Japanese Published Unexamined Patent Applications No. Hei 6-54186, No. Hei 6-225134, No. Hei 8-335267 and No. Hei 9-18709.
In case an instruction for output is issued to a printer connected to a network, it is generally performed to represent print data in a page description language (hereinafter called PDL). The printer connected to the network interprets a sent PDL, generates raster data of resolution suitable for the resolution of the printer and finally prints an image on paper.
FIG. 13 is a flowchart showing an example of printing operation in case processing for recognizing an image of which the printing is prohibited is executed by a printer. As described above, for technique for checking to see whether or not an image itself is an image of which the printing is prohibited, various methods are proposed. In case these techniques are applied to a printer connected to a network, a procedure shown in FIG. 13 for example is executed.
In an example shown in FIG. 13, PDL to be printed is rasterized in a step S81 and it is determined in a step S82 whether or not the rasterized image includes an image of which the printing is prohibited. In case an image of which the printing is prohibited is not included, the image rasterized in S81 is formed on paper for example in a step S84. Also, in case an image of which the printing is prohibited is included, the whole page or an area of the image of which the printing is prohibited is blanked in a step S83 or a message that printing is disabled is printed in S83.
In case the image of which the printing is prohibited is included in print data, the image can be determined by such processing so that it is not printed. However, in the processing shown in FIG. 13 or the conventional type recognition processing of an image of which the printing is prohibited, the raster image of all print data is made and afterward, it is determined whether or not an image of which the printing is prohibited is included.
As only a raster image is input to a copying machine and others, a conventional type recognition method can be adopted. However, in a printer for example, only after a raster image is made based upon a PDL as shown in FIG. 13, recognition processing can be executed. Therefore, until an image is actually printed and output after a raster image is made, processing for recognizing an image of which the printing is prohibited is executed and there is a problem that time required till printing and output is extended. When recognition processing is applied to a raster image for printing for one page for example, it takes approximately ten and several to several tens seconds and in consideration of the recent speedup of an output device, such long processing time cannot be allowed.